U.S. patent number 6,933,672 [Application Number 10/350,175] was granted by the patent office on 2005-08-23 for actively driven organic el device and manufacturing method thereof.
This patent grant is currently assigned to Idemitsu Kosan Co., Ltd.. Invention is credited to Chishio Hosokawa.
United States Patent |
6,933,672 |
Hosokawa |
August 23, 2005 |
Actively driven organic EL device and manufacturing method
thereof
Abstract
The present invention is a active-driving organic EL light
emission device comprising an organic EL element comprising an
organic luminous medium between an upper electrode and a lower
electrode, and a thin film transistor for driving this organic EL
element, wherein light emitted from the organic EL element is taken
out from the side of the upper electrode, and the upper electrode
comprises a main electrode formed of transparent conductive
material, and an auxiliary electrode formed of a low-resistance
material. According to the active-driving organic EL light emission
device of this structure, the numerical aperture can be made large.
Additionally, the sheet resistivity of the upper electrode can be
made low even if luminescence is taken out from the side of the
upper electrode. Thus, it is possible to provide an active-driving
organic EL light emission device making it possible to display
images having a high brightness and a homogenous brightness; and a
method for manufacturing the same.
Inventors: |
Hosokawa; Chishio (Sodegaura,
JP) |
Assignee: |
Idemitsu Kosan Co., Ltd.
(JP)
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Family
ID: |
18562444 |
Appl.
No.: |
10/350,175 |
Filed: |
January 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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784030 |
Feb 16, 2001 |
6538374 |
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Foreign Application Priority Data
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Feb 16, 2000 [JP] |
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2000-038756 |
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Current U.S.
Class: |
313/504; 313/503;
313/505 |
Current CPC
Class: |
H01L
27/3244 (20130101); H05B 33/12 (20130101); H01L
51/5228 (20130101); H01L 51/5234 (20130101); H01L
51/5206 (20130101); H01L 51/5212 (20130101); H01L
27/3246 (20130101); H01L 27/3279 (20130101); H01L
2251/5315 (20130101); H01L 27/3276 (20130101); H01L
51/5281 (20130101); H01L 51/5284 (20130101) |
Current International
Class: |
H01L
27/28 (20060101); H05B 33/12 (20060101); H01L
27/32 (20060101); H01L 51/52 (20060101); H01L
51/50 (20060101); H01J 001/88 () |
Field of
Search: |
;313/504,503,505,502,512,506 ;257/40,79,72 ;345/76,80 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2-37385 |
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Feb 1990 |
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JP |
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3-233891 |
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Oct 1991 |
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JP |
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7-111341 |
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Apr 1995 |
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JP |
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7-122360 |
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May 1995 |
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JP |
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7-122361 |
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May 1995 |
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JP |
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7-153576 |
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Jun 1995 |
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JP |
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7-312290 |
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Nov 1995 |
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JP |
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8-054836 |
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Feb 1996 |
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JP |
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8-109370 |
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Apr 1996 |
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JP |
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8-129359 |
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May 1996 |
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JP |
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8-227276 |
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Sep 1996 |
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JP |
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8-241047 |
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Sep 1996 |
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JP |
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10-189252 |
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Jul 1998 |
|
JP |
|
10-289784 |
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Oct 1998 |
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JP |
|
10-308284 |
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Nov 1998 |
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JP |
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10-335068 |
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Dec 1998 |
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JP |
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11-339968 |
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Dec 1999 |
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JP |
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Primary Examiner: O'Shea; Sandra
Assistant Examiner: Lee; Guiyoung
Attorney, Agent or Firm: Steptoe & Johnson LLP
Parent Case Text
This is a Continuation of application Ser. No. 09/784,0303 filed
Feb. 16, 2001 now U.S. Pat. No. 6,538,374.
Claims
What is claimed is:
1. An active-driving organic EL light emission device comprising:
an organic EL element comprising an organic luminous medium between
an upper electrode, and a lower electrode; and a thin film
transistor for driving the organic EL element; wherein light
emitted from the organic EL element is taken out from a side of the
upper electrode; the upper electrode comprises a main electrode
formed of a transparent conductive material, and an auxiliary
electrode formed of a low-resistance material; and the lover
electrode comprises a light-absorbing conductive material.
2. The device according to claim 1, further comprising an electric
switch comprising the thin film transistor and a transistor for
selecting a pixel, and a signal electrode line and a scanning
electrode line for driving the electric switch.
3. The device according to claim 1, wherein the transparent
conductive material is at least one material selected from the
group consisting of conductive oxides, light-transmissible metal
films, non-degenerate semiconductors, organic conductors, and
semiconductive carbon compound.
4. The device according to claim 3, wherein the organic conductor
is at least one material selected from the group consisting of
conductive conjugated polymers, oxidizing agent-added polymers,
reducing agent-added polymers, oxidizing agent-added low-molecules,
and reducing agent-added low-molecules.
5. The device according to claim 3, wherein the non-degeneracy
semiconductors are at least one material selected from the group
consisting of oxides, nitrides, and calchogenide compounds.
6. The device according to claim 3, wherein the carbon compounds
comprise at least one material selected from the group consisting
of amorphous carbon, graphite, and diamond-like carbon.
7. The device according to claim 1, wherein a plurality of
auxiliary electrodes are regularly placed in a plane.
8. The device according to claim 1, wherein a sectional shape of
the auxiliary electrode is an overhang form.
9. The device according to claim 1, wherein the auxiliary electrode
comprises a lower auxiliary electrode and an upper auxiliary
electrode.
10. The device according to claim 9, wherein the lover auxiliary
electrode and the upper auxiliary electrode comprise constituent
materials having different etching rates.
11. The device according to claim 9, wherein the lower auxiliary
electrode and the upper auxiliary electrode of the auxiliary
electrode, or one thereof is electrically connected to the main
electrode.
12. The device according to claim 1, wherein the auxiliary
electrode is formed on an interlayer dielectric constituting the
organic EL element.
13. The device according to claim 1, wherein the auxiliary
electrode is formed on an electrically insulating film for
insulating the lower electrode electrically.
14. The device according to claim 1, wherein the auxiliary
electrode is formed on an electrically insulating film for
insulating the thin film transistor electrically.
15. The device according to claim 1, wherein an active layer of the
thin film transistor comprises polysilicon.
16. The devices according to claim 1, wherein an interlayer
dielectric is formed on the thin film transistor, the lower
electorode of the organic EL element is deposited on the interlayer
dielectric, and the thin film transistor and the lower electrode
are electrically connected to each other through a via hole made in
the interlayer dielectric.
17. The device according to claim 1, wherein charges are injected
from the auxiliary electrode to the main electrode and transported
in parallel to a main surface of a substrate, and subsequently the
charges are infected to the organic luminous medium.
18. The device according to claim 1, wherein the sheet resistivity
of the main electrode is set to a value within the range of 1 K to
10 M.OMEGA./.quadrature..
19. The device according to claim 1, wherein the sheet resistivity
of the auxiliary electrode is set to a value within the range of
0.01 to 10 .OMEGA./.quadrature..
20. The device according to claim 1, further comprising a
fluorescent film and a color filter for color-converting the
taken-out light, or one thereof is arranged on the side of the
upper electrode.
21. The device according to claim 1, wherein a black matrix is
formed on a part of a color filter or a fluorescent film, and the
black matrix and the auxiliary electrode overlap with each other in
a vertical direction.
22. The device according to claim 1, wherein the auxiliary
electrode is formed on the main electrode, and an area of the
auxiliary electrode is smaller than an area of the main
electrode.
23. The device according to claim 1, wherein the auxiliary
electrode is embedded in a sealing member surrounding a periphery
thereof.
24. The device according to claim 1, wherein the auxiliary
electrode is closely arranged between the sealing member and the
main electrode.
25. The device according to claim 1, wherein the light-absorbing
conductive material is at least one selected from the group of
semiconductive carbon materials, organic compounds having a color
and conductive oxides having a color.
26. A method for manufacturing an active-driving organic EL light
emission device comprising an organic EL element having an organic
luminous medium between an upper electrode and a lover electrode
comprising a light-absorbing conductive material, and a thin film
transistor for driving the organic EL element, the method
comprising the steps of: forming the organic EL element; and
forming the thin film transistor, wherein during the step of
forming the organic EL element, the lower electrode comprising a
light-absorbing conductive material and the organic luminous medium
are formed and subsequently a main electrode is formed from a
transparent conductive material and the upper electrode is formed
by forming an auxiliary electrode from a low-resistance
material.
27. An active-driving organic EL light emission device comprising:
an organic EL element comprising an organic luminous medium between
an upper electrode and a lower electrode; and a thin film
transistor for driving the organic EL element; wherein light
emitted from the organic EL element is taken out from a aide of the
upper electrode; and the upper electrode comprises a main electrode
formed of a transparent conductive material, and an auxiliary
electrode formed of a low-resistance material, the auxiliary
electrode being electrically connected to the main electrode.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active-driving organic EL light
emission device (which may be referred to merely as an organic EL
device hereinafter) having a thin film transistor (which may be
referred to as a TFT). More specifically, the present invention
relates to an organic EL device used suitably for display equipment
and color displays for the people's livelihood and industries, and
the like.
In the present specification, the description "EL" means
"electroluminescence".
2. Description of the Related Art
Conventionally, it is known a simple-driving organic EL light
emission device which is simply driven by XY matrix electrodes to
display an image (Japanese Patent Application Laid-Open (JP-A) No.
37385/1990, JP-A No. 233891/1991 and the like) as an organic EL
light emission device (display).
However, in such a simple-driving organic EL light emission device,
the so-called line sequential driving is performed. Therefore, if
the number of scanning lines is several hundreds, required
instantaneous brightness is several-hundred times larger than
observed brightness so that the following problems arise.
(1) Since a driving voltage becomes not less than 2-3 times higher
than a direct-current constant voltage, luminous efficiency drops
or power consumption becomes large.
(2) Since the electrical current that passes instantaneously
becomes-several-hundred times larger, the organic luminous layer is
apt to deteriorate.
(3) Since the electrical current is very large in the same manner
as in the (2), a voltage-drop in the electrode wiring becomes
large.
Thus, in order to solve the problems that simple-driving organic EL
light emission devices have, various active-driving organic EL
light emission devices, wherein organic EL elements are driven by
TFTs (thin film transistors), ate suggested (JP-A No. 122360/1995,
JP-A No. 122361/1995, JP-A No. /153576/1995, JP-A No. 54836/1996,
JP-A No. 111341/1995, JP-A No. 312290/1995, JP-A No. 109370/1996,
JP-A No. 129359/1996, JP-A No. 241047/1996, JP-A No. 227276/1996,
JP-A No. 339968/1999, and the like).
Examples of the structure of such an active-driving organic EL
light emission device are shown in FIGS. 18 and 19. According to
such active-driving organic EL light emission devices, it is
possible to obtain advantages as follows: driving voltage is highly
lowered, luminous efficiency is improved and power consumption can
be reduced, as compared with simple-driving organic EL light
emission devices.
However, the following problems (1)-(3) are caused even in
active-driving organic EL light emission devices having
advantageous as described above.
(1) The aperture ratio of their pixels becomes small.
In an active-driving organic EL light emission device, at least one
TFT is fitted to each pixel on a transparent substrate and further
a great deal of scanning electrode lines and signal electrode lines
are disposed on the substrate to select appropriate TFTs and drive
them. Accordingly, there arises a problem that when light is taken
out from the side of the transparent substrate, the aperture ratio
of the pixels (the ratio of portions that emits light actually in
the pixels) becomes small since the TFTs and the various electrode
lines shut off the light. For example, in an active-driving organic
EL light emission device that has been developed recently, TFTs for
driving organic EL elements at a constant current are disposed
besides the above-mentioned two kinds of TFTs. Therefore, its
aperture ratio becomes smaller and smaller (about 30% or less). As
a result, dependently on the aperture ratio, the current density
that passes through the organic luminous medium becomes large,
causing a problem that the life span of the organic EL elements is
shortened.
This matter will be described in more detail, referring to FIGS.
10, 11 and 18. FIG. 10 shows a diagram of a circuit for
switch-driving the active-driving organic EL light emission device
100 illustrated in FIG. 18, and illustrates a state that gate lines
(scanning electrode lines) 50 (108 in FIG. 18) and source lines
(signal electrode lines) 51 are formed on the substrate and they
are in an XY matrix form. Common electrode lines 52 are disposed in
parallel to the source lines (signal electrode lines) 51. About
each pixel, a first TFT 55 and a second TFT 56 are fitted to the
gate lines 50 and the source lines 51. A capacitance 57 is
connected between the gate of the second TFT 56 and the common
electrode line 52 to hold the gate voltage at a constant value.
Therefore, an organic EL element 26 can be effectively driven by
applying the voltage held by the capacitance 57 to the gate of the
second TFT 56 shown in the circuit diagram of FIG. 10 and then
attaining switching.
The plan view shown in FIG. 11 is a view obtained by seeing, along
the plane direction, through switch portions and the like according
to the circuit diagram shown in FIG. 10.
Thus, the active-driving organic EL light emission device 100 has a
problem that when EL light is taken out from the side of lower
electrodes (ITO, indium tin oxide) 102 side, that is, the side of a
substrate 104 side, a TFT 106, a gate line 108, a source line (not
illustrated) and the like shut off EL light so that the aperture
ratio of pixels becomes small.
In an active-driving organic EL light emission device 204, as shown
in FIG. 19, wherein a TFT 200 and an organic EL element 202 are
arranged on the same plane, the TFT 200 and the like never block
off EL light. However, its aperture ratio of pixels is further
lowered, as compared with the active-driving organic EL light
emission device 100 shown in FIG. 18.
(2) The sheet resistivity of upper electrodes is large.
In the case that light is taken out from the side opposite to the
substrate, that is, the side of upper electrodes, the TFTs and the
like do not shut off the light to keep the aperture ratio large. As
a result, a high-brightness image can be obtained. However, when EL
light is taken out from the upper electrode side, in order to take
out the EL light effectively to the outside, it is necessary to
form the upper electrodes from transparent conductive material. For
this reason, the sheet resistivity of the upper electrodes exceeds,
for example, 20 .OMEGA./.quadrature., resulting in a serious
problem at the time of using large-area display.
In the case that light is emitted, for example, at a brightness of
300 nit from the entire surface of an EL light emission device
having a diagonal size of 20 inches (the ratio of length to
breadth, 3:4), it is necessary to send a large current having a
current of 3600 mA to the upper electrodes even if an organic
luminous material having a high luminous efficiency of 10 cd/A
(luminous power per unit amperage) is used in the organic
luminous-medium.
More specifically, the value of a voltage-drop based on the
resistances of the upper electrodes is represented by .SIGMA.nir
and calculated on the following formula.
N: (the total number of pixels in the longitudinal
direction).times.1/2,
r: the ohmic value (.OMEGA.) of the upper electrode in each pixel,
and
i: a constant current value(A) that flows through each pixel.
Therefore, if luminous efficiency, luminous brightness, the shape
of the pixels and the sheet resistivity of the upper electrodes are
set to, for example, 10 cd/A, 300 nit, 200.times.600 .mu.m square,
and 20 .OMEGA./.quadrature., respectively, the pixel current value
is 3.6.times.10.sup.-6 A. If the total number of the pixels in the
longitudinal direction is set to 2000, drop-voltage in the
longitudinal direction is 12V
(1/2.times.1000.times.1000.times.3.6.times.10.sup.-6.times.20.times.1/3).
This exceeds an allowable voltage range (10 V) for driving circuits
which are driven at a constant current. Thus, it is difficult to
emit light under the above-mentioned conditions.
In short, if the sheet resistivity of the upper electrodes is
large, voltage-drop, particularly at the center of the screen,
becomes large accordingly. As a result, a problem that brightness
is remarkably lowered becomes apparent. Incidentally, the following
is also attempted: amendment is made by using a circuit to make a
current value (brightness) constant for each pixel. However, this
attempt is insufficient.
(3) From the viewpoint of production, it is difficult to control
the ohmic value of the upper electrodes.
It is known that in order to set the resistivity of the upper
electrodes of an active-driving organic EL light emission device
having a diagonal size of several inches to 10 inches to a low
value, for example, 1.times.10.sup.-3 .OMEGA..multidot.cm or less
by using an ordinary material such as ITO or ZnO, it is necessary
to set heating temperature to 200.degree. C. or higher. However,
heat-resistance of ordinary organic luminous media is 200.degree.
C. or lower. Thus, it is necessary to set the heating temperature
to 200.degree. C. or lower. Accordingly, the value of the
resistivity of the upper electrodes cannot be controlled so that
the value may exceed 1.times.10.sup.-3 .OMEGA..multidot.cm. As a
result, a problem that the sheet resistivity becomes a high value
over 20 .OMEGA./.quadrature. occurs. In the case that plasma is
used for sputtering at the time of forming an oxide such as ITO or
IZO on the organic luminous medium to form the upper electrodes, a
problem that the organic luminous medium is damaged by the plasma
also arises.
In light of the above-mentioned problems, the present invention has
been made. Its object is to provide an organic active EL light
emission device making it possible to increase the aperture ratio
of respective pixels even if TFTs are disposed to drive organic EL
elements, reduce the sheet resistivity of upper electrodes even if
luminescence is taken out from the side of the upper electrodes,
and display an image having a high brightness and a homogeneous
brightness; and a method for manufacturing such an organic active
EL light emission device effectively.
SUMMARY OF THE INVENTION
[1] The present invention is an active-driving organic EL light
emission device comprising an organic EL element comprising an
organic luminous medium between an upper electrode and a lower
electrode, and a thin film transistor for driving this organic EL
element, wherein light emitted from the organic EL element (EL
light) is taken out from the side of the upper electrode, and the
upper electrode comprises a main electrode formed of a transparent
conductive material (embracing a transparent semiconductor
material), and an auxiliary electrode formed of a low-resistance
material.
Such a structure makes it possible to make a numerical aperture
large even if a TFT is set up and make the sheet resistivity of the
upper electrode reduced even if luminescence is taken out from the
side of the upper electrode.
It is also possible to improve brightness and further prolong the
life span of the organic luminous medium remarkably because of a
reduction in the density of electric current passing through the
organic luminous medium.
[2] The active-driving organic EL light emission device of the
present invention preferably comprises an electric switch
comprising the thin film transistor and a transistor for selecting
a pixel, and a signal electrode line and a scanning electrode line
for driving the electric switch.
Namely, it is preferred to comprise a scanning electrode line and a
signal electrode line arranged, for example, in an XY matrix form,
and an electric switch composed of a TFT connected electrically to
these electrode lines and a transistor for selecting a pixel.
Such a structure makes it possible to drive the organic EL element
effectively by selecting any pixel, applying a scanning signal
pulse and a signal pulse through the scanning electrode line and
the signal electrode line and thus performing switching-operation
of the electric switch comprising the TFT.
[3] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that the
transparent conductive material is at least one material selected
from the group consisting of a conductive oxide, a
light-transmissible metal film, a non-degeneracy semiconductor, an
organic conductor, and a semiconductive carbon compound.
Namely, the sheet resistivity of the upper electrode can be
reduced. It is therefore possible to use, in the main electrode,
not only transparent conductive material that has been
conventionally used but also transparent conductive material other
than it. Thus, the above-mentioned transparent conductive material
has-also been able to be used.
It is possible to use a non-degeneracy semiconductor and the like,
for example, which can be made into a film at a low temperature,
preferably 200.degree. C. or lower and more preferably 100.degree.
C. or lower. It is therefore possible to make heat damage of any
organic layer at the time of film-making small. Vapor deposition at
low temperature or wet coating can be attained by using the organic
conductor, the semiconductive carbon compound and the like.
[4] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that a
plurality of the auxiliary electrodes are regularly placed in a
plane.
For example, the resistance of the upper electrode can be uniformly
and effectively made low by arranging the auxiliary electrode in a
matrix, stripe and the like form.
[5] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that a
sectional shape of the auxiliary electrode is an overhang form.
Such a structure makes it possible to connect certainly the
auxiliary electrode electrically to the upper electrode, using a
site positioned below the overhanging upper portion (embracing a
conversely-tapered portion and the like) even if an insulating
organic layer is deposited on the auxiliary electrode.
[6] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that the
auxiliary electrode comprises a lower auxiliary electrode and an
upper auxiliary electrode.
Such a structure of the auxiliary electrode makes it possible to
easily connect the auxiliary electrode electrically to the main
element, using the lower auxiliary electrode or the upper auxiliary
electrode. Since the assistant is separated into the lower
auxiliary electrode and the upper auxiliary electrode as described
above, the overhanging form can easily be made.
[7] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that the
lower auxiliary electrode and the upper auxiliary electrode in the
auxiliary electrode comprise constituent materials having different
etching rates.
Such a structure makes it possible to form the overhang shape
easily by etching.
[8] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that the
lower auxiliary electrode and the upper auxiliary electrode in the
auxiliary electrode, or one thereof is electrically connected to
the main electrode.
Such a structure makes it possible to connect easily and certainly
the auxiliary electrode electrically to the main electrode so that
the resistance of the upper electrode can be made low.
[9] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that the
auxiliary electrode is formed on an interlayer insulating film for
forming the organic EL element, on the electrically insulating film
for insulating electrically the lower electrode, or on the
electrically insulating film for insulating electrically the
TFT.
Such a structure makes it possible to make the numerical aperture
in pixels wide.
[10] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that an
active layer of the TFT is made of polysilicon.
Such a structure makes, it possible to produce an active-driving
organic EL light emission device whose TFT has high endurance since
the active layer made of polysilicon has preferable resistance
against the amount of electricity.
[11] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that an
interlayer insulating film is formed on the TFT, the lower
electrode of the organic EL element is deposited on the interlayer
insulating film, and the TFT and the lower electrode are
electrically connected to each other through a via hole made in the
interlayer insulating film.
Such a structure makes it possible to obtain superior electrical
insulation between the TFT and the organic EL element.
[12] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that
charges are injected from the auxiliary electrode to the main
electrode and transported in parallel to a main surface of a
substrate, and subsequently the charges are injected to the organic
luminous medium.
Such a structure makes it possible to adopt a non-metal compound
for the main electrode so that the transparency of the main
electrode can be improved. The non-metal compound herein means, for
example, a non-degenerate semiconductor, an organic conductor, or a
semiconductive carbon compound that will be described later.
[13] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that the
sheet resistivity of the main electrode is set to a value within
the range of 1 K to 10 M.OMEGA./.quadrature.. In the structure of
the active-driving organic EL light emission device of the present
invention, it is preferred that the sheet resistivity of the
auxiliary electrode is set to a value within the range of 0.01 to
10 .OMEGA./.quadrature..
Adoption of such a structure for the respective electrodes makes it
possible to send electrical current giving a high luminous
brightness and cause a certain drop in the sheet resistivity of the
upper electrode.
[14] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that a
color filter for color-converting the taken-out light and a
fluorescent film, or one thereof is arranged on the side of the
upper electrode.
Such a structure makes it possible to color-convert luminescence
taken out from the upper electrode in the color filter or the
fluorescent film so that full-color display can be performed.
[15] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that a
black matrix is formed on a part of the color filter or the
fluorescent film, and the black matrix and the auxiliary electrode
overlap with each other in a vertical direction.
Such a structure makes it possible to suppress reflection of
outdoor daylight on the auxiliary electrode effectively by the
black matrix and make numerical aperture wide.
[16] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that the
auxiliary electrode is formed on the main electrode, and an area of
the auxiliary electrode is smaller than that of the main
electrode.
Such a structure makes it possible to form the auxiliary electrode
after the main electrode is formed. Therefore, it is easier to form
the auxiliary electrode.
[17] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that the
auxiliary electrode is embedded in a sealing member surrounding a
periphery thereof.
Such a structure does not cause the thickness of the organic EL
light emission device to be excessively large on the basis of the
thickness of the auxiliary electrode. Since the auxiliary electrode
can be formed beforehand in the sealing member, sealing based on
the sealing member and electrical connection between the auxiliary
electrode and the main electrode can be performed at the-same
time.
[18] In the structure of the active-driving organic EL light
emission device of the present invention, it is preferred that the
auxiliary electrode is closely arranged between the sealing member
and the main electrode.
Such a structure makes it possible to perform sealing based on the
sealing member and electrical connection between the auxiliary
electrode and the main electrode at the same time.
[19] According to another embodiment of the present invention, when
an active-driving organic EL light emission device is made, there
is used a method for manufacturing an active-driving organic EL
light emission device comprising an organic EL element having an
organic luminous medium between an upper electrode and a lower
electrode, and a thin film transistor for driving the organic EL
element, the method comprising the steps of forming the organic EL
element and forming the thin film transistor, wherein during the
step of forming the organic EL element, the lower electrode and the
organic luminous medium are formed and subsequently a main
electrode is formed from a transparent conductive material
(embracing a transparent semiconductor material) and the upper
electrode is formed by forming an electrically auxiliary electrode
formed from a low-resistance material.
According to such an embodiment, it is possible to provide an
active-driving organic EL light emission device wherein numerical
aperture is large even if the TFT is disposed and further the sheet
resistivity of the upper electrode is low even if luminescence is
taken out from the side of the upper electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of an active-driving organic EL light
emission device in a first embodiment.
FIG. 2 is a sectional view of an example of an active-driving
organic EL light emission device wherein an interlayer insulating
film in the first embodiment is removed.
FIG. 3 is a sectional view of an example wherein the arrangement of
auxiliary electrodes in the first embodiment is modified (No.
1).
FIG. 4 is a schematic view of an example wherein the auxiliary
electrodes in the first embodiment are regularly placed.
FIG. 5 is a sectional view of an active-driving organic EL light
emission device in a second embodiment.
FIG. 6 is a sectional view of an example wherein the arrangement of
auxiliary electrodes in the first embodiment is modified (No.
2).
FIG. 7 is a sectional view of an active-driving organic EL light
emission device in a third embodiment (No. 1).
FIG. 8 is a sectional view of an active-driving organic EL light
emission device in the third embodiment (No. 2).
FIG. 9 is a view supplied for explanation of a TFT.
FIG. 10 is a circuit diagram of an example of an active-driving
organic EL light emission device.
FIG. 11 is a seeing-through view of an active-driving organic EL
light emission device according to the circuit diagram shown in
FIG. 10 along its plan direction.
FIG. 12 is a view illustrating a part of the process of forming
TFTs.
FIG. 13 is a sectional view of an auxiliary electrode (No. 1).
FIG. 14 is a sectional view of an auxiliary electrode (No. 2).
FIG. 15 is a sectional view of an auxiliary electrode (No. 3).
FIG. 16 is a sectional view of an auxiliary electrode (No. 4).
FIG. 17 is a sectional view of a modification example of the
active-driving organic EL light emission device in the first
embodiment.
FIG. 18 is a sectional view of a conventional active-driving
organic EL light emission device (No. 1).
FIG. 19 is a sectional view of a conventional
active-driving-organic EL light emission device. It is a sectional
view of an auxiliary electrode (No. 2).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will be specifically described
hereinafter, referring to the drawings. In the drawings for
reference, the size and the shape of respective constituent
components and the arrangement relationship thereof are merely
illustrated schematically to such an extent that this invention can
be understood. Therefore, this invention is not limited to the
illustrated examples. In the drawings, hatching representing a
section may be omitted.
[First Embodiment]
As illustrated in FIG. 1, an active-driving organic EL light
emission device of a first embodiment is an active-driving organic
EL light emission device 61 having, on a substrate 10, TFTs 14
embedded in an electrically insulating film 12, an interlayer
insulating film (flattening film) 13 deposited on the TFTs 14,
organic EL elements 26, each of which comprises an organic luminous
medium 24 between an upper electrode 20 and a lower electrode 22,
and electric connecting portions 28 for connecting the TFT 14 with
the organic EL element 26.
In order to take out luminescence (EL light) of the organic element
26 and make the resistance of the upper electrode 20 low in the
first embodiment, the upper electrode 20 comprises a main electrode
16 made of transparent conductive material and an auxiliary
electrode 18 made of low-resistance material.
The following will describe constituent elements of the first
embodiment, and the like, referring appropriately to FIG. 2.
FIG. 2 illustrates an active-driving organic EL light emission
device 62 having a structure wherein the interlayer insulating film
(flattening film) 13 illustrated in FIG. 1 is removed. In FIG. 2,
the electrically insulating film 12 in which the TFTs 14 are
embedded functions as the interlayer insulating film.
1. Substrate
The substrate (which may be referred to as a supporting substrate)
in the organic EL display device is a member for supporting the
organic EL element, the TFTs, and the like. Therefore, it is
preferred that mechanical strength and dimensional stability
thereof are superior.
Specific examples of such a substrate include glass substrates,
metal substrates, ceramic substrates and plastic substrates
(polycarbonate resin, acrylic resin, vinyl chloride resins,
polyethylene terephthalate resin, polyimide resin, polyester resin,
epoxy resin, phenol resin, silicone resin, fluorine resin and the
like).
In order to avoid entry of water into the organic EL display
device, it is preferred that the substrate made of such a material
is subjected to moisture proof treatment or hydrophobic treatment,
based on the formation of an inorganic film or the application of a
fluorine resin.
In order to avoid entry of water into the organic luminous medium,
it is particularly preferred that the water content and the gas
permeability coefficient of the substrate are made small.
Specifically, it is preferred to set the water content of the
supporting substrate and the gas permeability coefficient thereof
to 0.0001% or less by weight, and 1.times.10.sup.-13
cc.multidot.cm/cm.sup.2.multidot.sec. cmHg or less,
respectively.
In order to take out EL light from the side opposite to the
substrate, that is, the side of the upper electrodes in the present
invention, the substrate does not necessarily needs to have
transparency.
2. Organic EL Element
(1) Organic Luminous Medium
The organic luminous medium can be defined as a medium comprising
an organic luminous layer wherein an electron and a hole are
recombined with each other so that EL light can be emitted. Such an
organic luminous medium can be made, for example, by laminating the
followings respective layers on an anode.
1 organic luminous layer
2 hole injection layer/organic luminous layer
3 organic luminous layer/electron injection layer
4 hole injection layer/organic luminous layer/electron injection
layer
5 organic semiconductor layer/organic luminous layer
6 organic semiconductor layer/electron barrier layer/organic
luminous layer
7 hole injection layer/organic luminous layer/adhesion improving
layer
Among these structures, the structure of the 4 is preferably used
in ordinary cases since the structure makes it possible to give a
higher luminous brightness and is superior in endurance.
1 Constituent Material
The luminous material in the organic luminous medium may be one or
a combination of two or more selected from p-quarterphenyl
derivatives, p-quinquephenyl derivatives, benzothiazole compounds,
benzoimidazole compounds, benozoxazole compounds, metal-chelated
oxinoid compounds, oxadiazole compounds, styrylbenzene compounds,
distyrylpyrazine derivatives, butadiene compounds, naphthalimide
compounds, perylene derivatives, aldazine derivatives, pyrazyline
derivatives, cyclopentadiene derivatives, pyrrolopyrrole
derivatives, styrylamine derivatives, coumalin compounds, aromatic
dimethylidene compounds, metal complexes having an 8-quinolinol
derivative as a ligand, and polyphenyl compounds.
Among these organic luminous materials, more preferred-are
4,4'-bis(2,2-di-t-butylphenylvinyl)biphenyl (abbreviated to
DTBPBBi), 4,4'-bis(2,2-diphenylvinyl)biphenyl (abbreviated to
DPVBi) and derivatives thereof as the aromatic dimethylidene
compounds.
It is also preferred to use a material wherein an organic luminous
material having a distyrylarylene skeleton and the like, as a host
material, is doped with an intensely fluoroscent colorant having a
color in from blue to red, as a dopant, for example, a coumalin
type material or a fluoroscent colorant that is equivalent to the
host. More specifically, it is preferred to use the above-mentioned
DPVBi and the like, as the host material, and
1,4-bis[{4-N,N'-diphenylamino}styryl]benzene (abbreviated to
DPAVB), as the dopant.
It is preferred to use, for the hole injection layer in the organic
luminous medium, a compound having a hole mobility of
1.times.10.sup.-6 cm.sup.2 /V.multidot.second or more and an
ionization energy of 5.5 eV or less. The hole mobility is measured
in the case that a voltage of 1.times.10.sup.4 to 1.times.10.sup.6
V/cm is applied thereto. The deposit of such a hole injection layer
makes injection of holes into the organic luminous layer
satisfactory so that high luminous brightness can be obtained or
low-voltage driving can be attained.
Specific examples of the constituent material of such a hole
injection layer include organic compounds such as porphyrin
compounds, aromatic tertiary amine compounds, styryl amine
compounds, aromatic dimethylidene compounds, and condensed aromatic
ring compounds, for example,
4,4'-bis[N-(1-naphtyl)-N-phenylamino]biphenyl (abbreviated to NPD)
and 4,4',4"-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine
(abbreviated to MTDATA).
As the constituent material of the hole injection layer, an
inorganic compound such as p-type Si or p-type SiC is preferably
used.
An organic semiconductor layer having a conductivity of
1.times.10.sup.-10 S/cm or more is preferably arranged between the
hole injection layer and an anode layer, or between the hole
injection layer and the organic luminous layer. The arrangement of
such an organic semiconductor layer makes injection of the holes
into the organic luminous layer more satisfactory.
It is also preferred to use, for the electron injection layer in
the organic luminous medium, a compound having an electron mobility
of 1.times.10.sup.-6 cm.sup.2 /V.multidot.second or more and an
ionization energy of more than 5.5 eV. The electron mobility is
measured in the case that a voltage of 1.times.10.sup.4 to
1.times.10.sup.6 V/cm is applied thereto. Deposit of such an
electron injection layer makes injection of electrons into the
organic luminous layer satisfactory so that high luminous
brightness can be obtained or low-voltage driving can be
attained.
Specific example of the constituent material of such an electron
injection layer include a metal complex of 8-hydroxyquinoline (Al
chelate: Alq), derivatives thereof or oxazole derivatives and the
like.
The adhesion improving layer in the organic luminous medium may be
regarded as one form of the electron injection layer, that is, a
layer which is one of the electron injection layers and is made of
a material that is particularly good in adhesiveness to the
cathode. This layer is preferably made of a metal complex of
8-hydroxyquinoline, a derivative thereof and the like.
It is also preferred to deposit an organic semiconductor layer
having a conductivity of 1.times.10.sup.-10 S/cm or more to contact
the electron injection layer. The deposit of such an organic
semiconductor layer makes the injection of electrons into the
organic luminous layer more satisfactory.
2 Thickness
The thickness of the organic luminous medium is not particularly
limited. It is preferred to set the thickness to a value within the
range of, for example, 5 nm to 5 .mu.m.
The reason for this is as follows. If the thickness of the organic
luminous medium is below 5 nm, luminous brightness or endurance may
be lowered. On the other hand, if the thickness of the organic
luminous medium is over 5 .mu.m, the value of applied voltage may
be raised.
Accordingly, the thickness of the organic luminous medium is
preferably set to a value within the range of 10 nm to 3 .mu.m, and
more preferably set to a value within the range of 20 nm to 1
.mu.m.
(2) Upper Electrodes
1 Structure 1
As shown in FIG. 1, in the first embodiment, the upper electrode 20
is characterized by being composed of the main electrode 16
comprising transparent conductive material, and the auxiliary
electrode 18 comprising low-resistance material.
The sheet resistivity of the upper electrode 20 can be remarkably
reduced by arranging not only the main electrode 16 but also the
auxiliary electrode 18 comprising low-resistance material in the
above-mentioned manner. Therefore, the organic EL element 26 can be
driven at a low voltage and power consumption can be reduced.
The main electrode 16 shown in FIG. 1 is made of transparent
conductive material, for example, a material having a
transmissivity of 10% or more and preferably having a
transmissivity of 60% or more. Therefore, EL light can be
effectively taken out through the main electrode 16 to the outside.
Thus, even if the TFT 14 and the like are set up, the aperture
ratio of the pixels 31 can be made large.
2 Structure 2
As shown in FIGS. 13 to 15, about the structure of the auxiliary
electrode 18 in the upper electrode 20, the auxiliary electrode 18
is preferably composed of an upper auxiliary electrode 17 and a
lower auxiliary electrode 19.
Such a structure makes it possible to connect the lower auxiliary
electrode 19 electrically to the main electrode 16 even if the
upper auxiliary electrode 17 is electrically insulated. Contrarily,
even if the lower auxiliary electrode 19 is electrically insulated,
the upper electrode 17 can be connected electrically to the main
electrode 16.
Such a structure also makes it possible to use different
constituent materials to make the respective electrodes. Therefore,
the electrical connection between the auxiliary electrode 18 and
the main electrode 16 is made more certain. In the case that the
main electrode 16 is electrically connected to the upper auxiliary
electrode 17 comprising a metal material through the lower
auxiliary electrode 19 comprising a semiconductor material having
relatively good capability of connecting any transparent oxide
conductive material as well as any metal, for example, an indium
zinc oxide (IZO) as an amorphous inorganic oxide, the electrical
connection between the auxiliary electrode 18 and the main
electrode 16 is made more certain than, for example, in the case
that the main electrode 16 comprising a transparent oxide
conductive material is electrically connected directly to the
auxiliary electrode 18 comprising a metal material.
Furthermore, such a structure makes it possible to use constituent
materials having different etching properties to make the
respective auxiliary electrodes. Therefore, the sectional shape of
the auxiliary electrode 18 can easily be made into an overhang form
as described below.
3 Structure 3
As shown in FIGS. 13 to 16, about the structure of the auxiliary
electrode 18 in the upper electrode 20, the sectional shape of the
auxiliary electrode 18 is preferably made into an overhang
form.
The reason for this is that the auxiliary electrode can be
electrically connected to the main electrode 16 through the
overhanging lower portion even if an insulating film is deposited
on the auxiliary electrode 18.
Specifically, if after the formation of the auxiliary electrode 18
an insulating film or an organic luminous medium is formed by vapor
deposition and the like and further the main electrode 16 is
formed, the insulating film covers the auxiliary electrode 18 so
that it may become difficult to connect the auxiliary electrode 18
electrically to the main electrode 16.
On the other hand, in the case that the sectional shape of the
auxiliary electrode 18 is in the overhang form, an insulating film,
even when being deposited by vapor-deposition and the like, is not
easily adhered to the side of the auxiliary electrode 18. Using
this naked side of the auxiliary electrode 18, electrical
connection to the main electrode 16 can be made sure.
For example, in FIG. 14, the upper electrode 17 is electrically
insulated by the organic luminous medium 24 and the like while the
lower electrode 19 is electrically connected to the main electrode
16. This demonstrates connection-easiness of the auxiliary
electrode 18 originating from this structure.
The sectional shape of the auxiliary electrode 18 can easily be
made into an overhang form by composing the auxiliary electrode 18
of the lower and upper electrodes 19 and 17 and making the two
electrodes 19 and 17 from constituent materials having different
etching rates. Specifically, it is preferred to make the lower
auxiliary electrode 19 from a metal material such as Al or Al
alloy, and make the upper auxiliary electrode 17 from a non-metal
material such as silica, alumina, Sinitride, Cr nitride, Ta nitride
or W nitride.
The lower auxiliary electrode 19 and the upper auxiliary electrode
17 are made from, for example, Al and Cr, respectively, and Cr is
etched with an ammonium cerium nitrate solution in a
photolithographic manner. Thereafter, Al is further etched with a
mixed solution of phosphoric acid, nitric acid, and acetic acid, so
that only Al of the lower auxiliary electrode 19 is over-etched.
Thus, an overhang can easily be obtained.
Examples of such an overhang are shown in FIGS. 13 to 16. The
overhang may have various shapes. It is allowable to use the
auxiliary electrode 18 in an overhang form having a bilayer
structure composed of the lower auxiliary electrode 19 and the
upper auxiliary electrode 17, and as shown in FIG. 16(e), an
auxiliary electrode 18 in an overhang form having a three-layer
structure.
Arrows in FIGS. 13 to 16 represent the projecting direction of the
overhangs.
4 Structure 4
As shown in FIG. 4, about the structure of the auxiliary electrodes
18 in the upper electrode 20, it is preferred that the auxiliary
electrodes 18, when are viewed from the above, are regularly placed
in a plane.
This makes it possible to make the ohmic value of the upper
electrodes highly and uniformly low. The regularly placement of the
auxiliary electrodes 18 makes the production thereof easy.
5 Structure 5
As shown in FIGS. 1 and 2, about the structure of the auxiliary
electrodes 18 in the upper electrode 20, it is preferred that the
auxiliary electrode 18, when viewed from the above, is arranged
between the lower auxiliary electrodes 22 adjacent to each other.
This is demonstrated by, for example, arrangement of the auxiliary
electrode 18 between adjacent pixels 31 drawn by dot lines in FIG.
2.
In short, such arrangement of the auxiliary electrode 18 makes it
possible to obtain a higher luminous brightness without making the
numerical aperture of the pixels 31 narrow.
It is preferred as another arrangement of the auxiliary electrodes
18 that in the case that a color filter or a fluorescent film 60
shown in FIG. 5 is arranged and further a black matrix (light
shading portions) is arranged in perpendicular direction positions
corresponding to the gaps between lower electrodes 22, the
auxiliary electrodes 18 are arranged in the manner that the light
shading portion of the black matrix and the auxiliary electrode
overlap with each other in the perpendicular direction.
Such a structure does not make the aperture ratio of pixels narrow
even if the black matrix is arranged and makes it possible to
prevent reflection light on the auxiliary electrodes
effectively.
6 Structure 6
As shown in FIGS. 1 and 2, about the structure of the auxiliary
electrodes 18 in the upper electrode 20, it is preferred that the
auxiliary electrodes 18 are deposited on the electrically
insulating film 12 for insulating the TFTs 14 and the interlayer
insulating film (flattening film) 13, or either one of the
insulating film 12 or 13.
Such a structure makes it possible to reduce electric capacity made
between the auxiliary electrode and wiring related to the TFT.
Thus, switching operation of the organic EL elements can become
fast.
Further, as shown in FIG. 3, as another arrangement of the
auxiliary electrodes 18, it is preferred that an electrically
insulating film 25, which is different from the interlayer
insulating film 13, is arranged between adjacent lower electrodes
22 and the auxiliary electrodes 18 are formed on the insulating
film 25.
Such a structure makes it possible to reduce a short circuit
between the lower electrode 22 and the upper electrode 20 that is
caused in a step of the lower electrode 22, or a leakage. Thus,
image defects can be reduced.
As shown in FIG. 6, as the arrangement of the auxiliary electrodes
18, it is preferred that the auxiliary electrodes 18 are formed on
the main electrodes 16 and the area of the auxiliary electrodes 18
is made smaller than that of the main electrodes 16.
Such a structure does-not make the aperture ratio of pixels narrow,
and makes it easy to form the auxiliary electrodes and adjust the
sheet resistivity of the auxiliary electrodes.
Needles to say, the structure 6 about the arrangement relative to
the interlayer insulating film and the like satisfies the
arrangement of the structure 5 since the auxiliary electrode 18 is
arranged between the adjacent lower electrodes 22.
7 Constituent Material 1
The upper electrode 20 (the main electrode 16 and the auxiliary
electrode 18) in FIG. 1 and the like corresponds to an anode layer
or a cathode layer dependently on the structure of the organic EL
element. In the case of the anode layer, a constituent material
having a large work function, for example, a work function of 4.0
eV or more is preferably used since holes are easily injected
therein. In the case of the cathode layer, a constituent material
having a small work function, for example, a work function of less
than 4.0 eV is preferably used since electrons are easily injected
therein.
On the other hand, in order to take out luminescence to the outside
in the first embodiment, it is essential that the constituent
material of the main electrode 16 in the upper electrode 20 has
given transparency.
Thus, in the case that the upper electrode 20 corresponds to the
anode layer, the constituent material of the main electrode 16 may
be specifically one or a combination of two or more selected from
indium tin oxide (ITO), indium zinc oxide (IZO), copper iodide
(CuI), tinoxide (SnO.sub.2), zinc oxide (ZnO), antimony oxide
(Sb.sub.2 O.sub.3, Sb.sub.2 O.sub.4, and Sb.sub.2 O.sub.5),
aluminum oxide (Al.sub.2 O.sub.3) and the like.
In order to make the resistance of the main electrode 16 low
without damaging the transparency thereof, it is preferred to add
one or a combination of two ore more selected from Pt, Au, Ni, Mo,
W, Cr, Ta, Al metal and the like in the form of the thin film.
In the first embodiment, the sheet resistivity of the upper
electrode 20 can be reduced by not only the transparent material
but also the auxiliary electrode 18. For the main electrode 16,
therefore, at least one constituent material can be selected from
light transparent metal films, non-degenerate semiconductors,
organic conductors, semiconductive carbon compounds and the
like.
For example, for the organic conductor, preferred is a conductive
conjugated polymer, an oxidizing agent-added polymer, a reducing
agent-added polymer, an oxidizing agent-added low-molecule, or a
reducing agent-added low-molecule.
The oxidizing agent added to the organic conductor may be a Lewis
acid such as iron chloride, antimony chloride or aluminum chloride.
The reducing agent added to the organic conductor maybe an alkali
metal, an alkali earth metal, a rare earth metal, an alkali
compound, an alkali earth compound, a rare earth metal compound,
and the like. The conductive conjugated polymer may be polyaniliine
or a derivative thereof, polythiophene or a derivative, a Lewis
acid added amine compound layer, and the like.
Preferred specific examples of the non-degenerate semiconductor
include oxides, nitrides, and chalcogenide compounds.
Preferred specific examples of the carbon compound include
amorphous C, graphite, and diamond-like C.
Preferred specific examples of the inorganic semiconductor include
ZnS, ZnSe, ZnSSe, MgS, MgSSe, CdS, CdSe, CdTe and CdSSe and the
like.
8 Constituent Material 2
It is necessary that the auxiliary electrode 18 shown in FIG. 1 and
the like is made of low-resistance material. It is preferred to use
low-resistance material having a specific resistance within the
range of, for example, 1.times.10.sup.-5 to 1.times.10.sup.-3
.OMEGA..multidot.cm.
The reason for this is as follows. A material having a specific
resistance of less than 1.times.10.sup.-5 .OMEGA..multidot.cm
cannot be easily realized. On the other hand, if the specific
resistance is over 1.times.10.sup.-3 .OMEGA..multidot.cm, it may be
difficult to make the resistance of the upper electrode low.
Therefore, the specific resistance of the low-resistance material
constituting the auxiliary electrode is more preferably set to a
value within the range of 2.times.10.sup.-5 to 5.times.10.sup.-4
.OMEGA..multidot.cm, and still more preferably set to a value
within the range of 2.times.10.sup.-5 to 1.times.10-4
.OMEGA..multidot.cm.
The sheet resistivity of the auxiliary electrode 18 is preferably
set to a value within the range of 0.01 to 10 .OMEGA./.quadrature..
The reason for this is as follows. If the sheet resistivity is
below 0.01 .OMEGA./.quadrature., it may be necessary to make the
upper electrode thick or the material for use may be excessively
restricted. On the other hand, the sheet resistivity is over 10
.OMEGA./.quadrature., the resistance of the upper electrode may not
be easily made low or the upper electrode becomes too thin to be
formed.
Therefore, the sheet resistivity of the auxiliary electrode is more
preferably set to a value within the range of 0.01 to 10
.OMEGA./.quadrature. and still more preferably set to a value
within the range of 0.01 to 5 .OMEGA./.quadrature..
As a preferred low-resistance material constituting the auxiliary
electrode 18, various metals used in wiring electrodes are
preferably used. Specifically, it is preferred to contain one or a
combination of two or more selected from Al, alloys of Al and a
transition metal (Sc, Nb, Zr, Hf, Nd, Ta, Cu, Si, Cr, Mo, Mn, Ni,
Pd, Pt and W and the like), Ti, titanium nitride (TiN), and the
like.
Such low-resistance material is more preferably Al or an alloy of
Al and a transition metal. In the case that an alloy of Al and a
transition metal is used, the content by percentage of the
transition metal is preferably 10% or less by atom (referred to as
at. % or atm %), more preferably 5% or less by atom, and still more
preferably 2% or less by atom. This is because as the transition
metal content is smaller, the sheet resistivity of the auxiliary
electrode can be made lower.
In the case that the above-mentioned metal is used as the main
component, the amounts of used Al, Ti and TiN are preferably
90-100% by atom, 90-100% by atom, and 90-100% by atom,
respectively.
When two or more of these metals are used, the blend ratio thereof
is arbitrary. The Ti content is 10% or less by atom is preferred,
for example, when a mixture of Al and Ti is used.
Furthermore, plural layers comprising these metals may be laminated
to make the auxiliary electrode 18.
9 Thickness
The thickness of the main electrode 16 and the auxiliary electrode
18 shown in FIG. 1 and the like is preferably decided under
consideration of the sheet resistivity and the like. Specifically,
the thickness of each of the main electrode 16 and the auxiliary
electrode 18 is preferably a value of 50 nm or more, more
preferably a value of 100 nm or more, and still more preferably a
value within the range of 100 to 5,000 nm.
The reason for this is as follows. Setting the thickness of the
main electrode 16 and the auxiliary electrode 18 to a value within
such a range makes it possible to obtain a uniform thickness
distribution and a transmissivity of 60% or more about light
emission (EL light). Moreover, the sheet resistivity of the upper
electrode 20 comprising the main electrode 16 and the auxiliary
electrode 18 can be made to 15 .OMEGA./.quadrature. or less, and
more preferably 10 .OMEGA./.quadrature. or less.
(3) Lower Electrode
1 Constituent Material
The lower electrode 22 shown in FIG. 1 and the like also
corresponds to an anode layer or a cathode layer dependently on the
structure of the organic EL display device. When the lower
electrode 22 corresponds to, for example, a cathode, it is
preferred to use a metal, alloy or electrically conductive compound
which has a small work function (for example, less than 4.0 eV), a
mixture thereof, or a substance containing it.
Specifically, a single or a combination of two or more selected
from the following electrode materials is preferably used: sodium,
sodium-potassium alloys, cesium, magnesium, lithium,
magnesium-silver alloys, aluminum, aluminum oxides,
aluminum-lithium alloys, indium, rare earth metals, mixture of any
one of these metals and an organic luminous medium material,
mixtures of any one of these metals and-an electron injection layer
material, and the like.
Moreover, since luminescence is taken out from the side of the
upper electrodes 20 in the present invention, the constituent
material of the lower electrodes 22 does not necessarily need to
have transparency. In a preferred embodiment, the lower electrode
is made of a light-absorbing conductive material. Such a structure
makes it possible to improve contrast of the organic EL display
device still more. Preferred examples of the light-absorbing
conductive material in this case include semiconductive carbon
materials, organic compounds having a color, combinations of the
above-mentioned reducing agent and oxidizing agent, and conductive
oxides having a color (transition metal oxides such as VO.sub.x,
MoO.sub.x, and WO.sub.x).
2 Thickness
In the same way as for the upper electrode 20, the thickness of the
lower electrode 22 is not particularly limited, either.
Specifically, the thickness is preferably a value within the range
of 10 to 1,000 nm, and more preferably a value within the range of
10 to 200 nm.
(4) Interlayer Insulating Film
The interlayer insulating film (electrically insulating film) 13 in
the organic EL display device 61 shown in. FIG. 1 is present near
or around the organic EL element 26, and is used to make the whole
of the organic EL display device 61 minute and prevent a short
circuit between the lower electrode 22 and the upper electrode 20
in the organic EL element 26. When the organic EL element 26 is
driven by the TFT 14, the interlayer insulating film 13 is also
used as an undercoat for protecting the TFT 14 and for depositing
the lower electrode 22 of the organic EL element 26 flatly.
For this reason, the interlayer insulating film 13 may be referred
to as a different name such as a barrier, a spacer, or a flattening
film, if necessary. In the present invention, the interlayer
insulating film embraces them.
1 Constituent Material
Examples of the constituent material used in the interlayer
insulating film 13 shown in FIG. 1 usually include acrylic resin,
polycarbonate resin, polyimide resin, fluorinated polyimide resin,
benzoguanamine resin, melamine resin, cyclic polyolefin, Novolak
resin, polyvinyl cinnamate, cyclic rubber, polyvinyl chloride
resin, polystyrene, phenol resin, alkyd resin, epoxy resin,
polyurethane resin, polyester resin, maleic acid resin, and
polyamide resin and the like.
In the case that the interlayer insulating film is made of an
inorganic oxide, preferred examples of the inorganic oxide include
silicon oxide (SiO.sub.2 or SiO.sub.x), aluminum oxide (Al.sub.2
O.sub.3 or AlOx), titanium oxide (TiO.sub.2 or TiO.sub.x), yttrium
oxide (Y.sub.2 O.sub.3 are YO.sub.x), germanium oxide (GeO.sub.2 or
GeO.sub.x), zinc oxide (ZnO), magnesium oxide (MgO), calcium oxide
(CaO), boric acid (B.sub.2 O.sub.3), strontium oxide (SrO), barium
oxide (BaO), lead oxide (PbO), zirconia (ZrO.sub.2), sodium oxide
(Na.sub.2 O), lithium oxide (Li.sub.2 O), and potassium oxide
(K.sub.2 O). The value x in the inorganic compound is a value
within the range of 1.ltoreq.x.ltoreq.3.
In the case that heat-resistance is particularly required, it is
preferred to use acrylic resin, polyimide resin, fluorinated
polyimide, cyclic polyolefin, epoxy resin, or inorganic oxide.
These interlayer insulating films, when being organic, can be
worked into a desired pattern by introducing a photosensitive group
thereto and using photolithography method, or can be formed into a
desired pattern by printing.
2 Thickness of the Interlayer Insulating Film, and the Like
The thickness of the interlayer insulating film depends on the
minuteness of display, a fluorescent medium combined with the
organic EL element, or unevenness of a color filter, and is
preferably a value within the range of 10 nm to 1 mm.
This is because such a structure makes it possible to make the
unevenness of the TFT and the like sufficiently flat.
Accordingly, the thickness of the interlayer insulating film is
more preferably a value within the range of 100 nm to 100 .mu.m,
and still more preferably a value within the range of 100 nm to 10
.mu.m.
3 Forming Method
The method for forming the interlayer insulating film is not
particularly limited. The layer is preferably deposited by, for
example, spin coating method, casting method, screen-printing
method and the like, or is preferably deposited by sputtering
method, vapor-deposition method, chemical vapor deposition method
(CVD method), ion plating method, and the like.
3. Thin Film Transistor (TFT)
(1) Structure
As shown in FIG. 9, one example of the organic active EL light
emission device 68 has, on a substrate 10, a TFT 14 and an organic
EL element 26 driven by this TFT 14.
An interlayer insulating film 13 whose surface (upper surface) is
made flat is arranged between the TFT 14 and a lower electrode 22
of the organic EL element 26. A drain 47 of the TFT 14 and the
lower electrode 22 of the organic EL element 26 are electrically
connected to each other through a contact hole 54 made in this
interlayer insulating film 13.
As shown in FIG. 10, scanning electrode lines (Yj-Yj+n) 50 and
signal electrode lines (Xi-Xi+n) 51 arranged in an XY matrix are
electrically connected to the TFT 14. Furthermore, common electrode
lines (Ci-Ci+n) 52 are electrically connected in parallel to the
TFTs 14.
It is preferred that these electrode lines 50, 51 and 52 are
electrically connected to the TFT 14 and they, together with a
capacitance 57, constitute an electric switch for driving the
organic EL element 26. Specifically, it is preferred that this
electric switch is electrically connected to the scanning electrode
line, the signal electrode line and the like, and comprises, for
example, at least one first transistor (which may be referred to as
Tr1 hereinafter) 55, a second transistor (which may be referred to
as Tr2 hereinafter) and the capacitance 57.
It is preferred that the first transistor 55 has a function for
selecting a luminous pixel and the second transistor 56 has a
function for driving the organic EL element.
As shown in FIG. 9, an active layer 44 in the first transistor
(Tr1) 55 and the second transistor (Tr2) 56 is a portion shown as
n+/i/n+. It is preferred that the two sides n+ are composed of
semiconductor regions 45 and 47 doped into the n type and i
therebetween is composed of a non-doped semiconductor region
46.
The semiconductor regions doped with the n type are a source 45 and
the drain 47, respectively. They, together with a gate 46 deposited
through a gate oxide film on the non-doped semiconductor region,
constitute the first and second transistors 55 and 56.
In the active layer 44, the semiconductor regions 45 and 47 doped
into the n type may be doped into the p type, instead of the n
type, so as to make a structure of p+/i/p+.
The active layer 44 in the first transistor (Tr1) 55 and the second
transistor (Tr2) 56 is preferably made of an inorganic
semiconductor such as polysilicon or an organic semiconductor such
as thiophene oligomer or poly(P-phenylenevinylene). Polysilicon is
a particularly preferred material since it is far more stable
against electricity than amorphous Si (.alpha.-Si).
Besides, the organic EL element 26 is deposited through the
interlayer insulating film (flattening film) 13 on the TFT 14
formed on the surface of the substrate 10 in the examples shown in
FIGS. 1 and 9. As shown in FIG. 17, it is also preferred to form
the TFT on the back surface of the substrate, form the organic EL
element on the surface of the substrate and connect the TFT 14 and
the lower electrode of the organic EL element 26 electrically to
each other through a via hole 28 made in the substrate 10 and the
interlayer insulating film (flattening film) 13.
Such a structure makes it possible to keep better electrical
insulation between the TFT 14 and the organic EL element 26. In
this example, the interlayer insulating film(flattening film) 13 is
deposited on the substrate 10. However, the interlayer insulating
film 13 may be omitted since both surfaces of the substrate 10 have
superior flatness.
(2) Driving Method
The following will describe the method for driving the organic EL
element by the TFT 14. As shown in FIG. 10, the TFT 14 comprises
the first transistor (Tr1) 55 and the second transistor (Tr2) 56,
and further the TFT combined with the capacitance 57 constitutes a
part of the electric switch.
Therefore, a scanning pulse and a signal pulse are inputted through
the XY matrix to this electric switch to perform switch operation,
so that the organic EL element 26 connected to this electric switch
can be driven. Thus, light emission from the organic EL element 26
is caused or stopped by the electric switch comprising the TFT 14
and the capacitance 57, so that an image can be displayed.
Specifically, a desired first transistor 55 is selected by a
scanning pulse transmitted through the scanning electrode line
(which may be referred to as a gate line) (Yj-Yj+n) 50 and a signal
pulse transmitted through the signal electrode line (Xi-Xi+n) 51,
so as to supply given electrical charges to the capacitance 57
formed between the common electrode line (Ci-Ci+n) 52 and the
source 45 of the first transistor (Tr1) 55.
In this way, the gate voltage of the second transistor (Tr2) 56
turns into a constant value and the second transistor (Tr2) 56
turns into an ON state. Since in this ON state the gate voltage is
held at a given value until a next gate pulse is transmitted,
electric current continues to be supplied to the lower electrode 22
connected to the drain 47 of the second transistor (Tr2) 56.
The organic EL element 26 is effectively driven by direct-current
supplied through the lower electrode 22. Thus, by the effect of the
direct-current driving, the driving voltage for the organic EL
element 26 can be highly reduced and the luminous efficiency
thereof is improved. Moreover, power consumption can be
reduced.
[Second Embodiment]
As shown in FIG. 5, the active-driving organic EL light emission
device of the second embodiment is an active-driving organic EL
light emission device 64 comprising, on the substrate 10, the TFT
14 embedded in the electrically insulating film 12, the organic EL
element 26 comprising the organic luminous medium 24 between the
upper electrode 20 and the lower electrode 22, and the electrically
connecting portion (via hole) 28 for connecting the TFT 14 and the
organic EL element 26 to each other.
The second embodiment is characterized in that, the upper electrode
20 is composed of the main electrode 16 and the auxiliary electrode
18, and further above the upper electrode 20 is set up a color
filter or fluorescent film 60 for color-converting EL light taken
out from the side of the upper electrode 20. (An arrow in FIG. 5
represents a direction along which the light is taken out.)
The following will describe the characteristic parts and the like
of the second embodiment, referring appropriately to FIG. 5.
(1) Color Filter
1 Structure
The color filter is set up to decompose or cut light to improve
color adjustment or contrast, and comprises a colorant layer
consisting only of a colorant, or a lamination wherein a colorant
is dissolved or dispersed in a binder resin. The colorant referred
to herein embraces a pigment.
The structure of the color filter preferably comprises a blue,
green or red colorant. Combination of such a color filter with the
organic EL element emitting white light makes it possible to obtain
three primary colors of light, that is, blue, green and red, and to
attain full-color display.
The color filter is preferably patterned by printing method or
photolithography method in the same manner as for the fluorescence
medium.
2 Thickness
The thickness of the color filter is not particularly limited so
far as the thickness causes sufficient receipt (absorption) of
luminescence from the organic EL element and does not damage
color-converting function. The thickness is preferably, for
example, a value within the range of 10 nm to 1 mm, more preferably
a value within the range of 0.5 .mu.m to 1 mm, and still more
preferably a range within the range of 1 .mu.m to 100 .mu.m.
(2) Fluorescent Medium
1 Structure
The fluorescent medium in the organic EL display device has a
function for absorbing luminescence from the organic EL element and
emitting fluorescence having a longer wavelength, and comprises
layer-form matters separated and arranged in a plane. The
respective fluorescent medium are preferably arranged
correspondingly to luminescence areas of the organic EL elements,
for example, positions where the lower electrode and the upper
electrode cross each other. When the organic luminous layer at the
portion where the lower electrode and the upper electrode cross
each other emits light, such a structure makes it possible that the
respective fluorescent media receive the light to take out light
rays having different colors (wavelengths) to the outside.
Particularly when the organic EL element emits blue light and the
light can be converted to green or red luminescence by the
fluorescent medium, the three primary colors of light, that is,
blue, green and red can be obtained even from the single organic EL
element. Thus, full-color display can be attained, and is
preferable.
In order to shut off luminescence from the organic EL element and
light from the respective fluorescent medium to improve contrast or
reduce dependency on the angle of field, it is also preferred to
arrange a light shading layer (black matrix).
The fluorescent medium may be combined with the above-mentioned
color filter to prevent a drop in contrast based on outdoor
daylight.
2 Forming Method
In the case that the fluorescent medium comprises mainly a
fluorescent colorant, the medium is preferably made to a film by
vacuum deposition or sputtering through a mask for obtaining a
desired fluorescent medium pattern.
On the other hand, in the case that the fluorescent medium
comprises a fluorescent colorant and a resin, the fluorescent
colorant, the resin and an appropriate solvent are mixed, dispersed
or solubilized into a liquid and then the liquid is made to a film
by spin coating, roll coating, casting and the like method.
Thereafter, the fluorescent medium is preferably formed by forming
a desired fluorescent medium pattern using photolithography method,
or by forming a desired pattern by screen printing and the like
method.
3 Thickness
The thickness of the fluorescent medium is not particularly limited
if the thickness causes sufficient receipt (absorbance) of
luminescence from the organic EL element and does not damage the
function for generating fluorescence. The thickness is preferably a
value within the range of 10 nm to 1 mm, more preferably a value
within the range of 0.5 .mu.m to 1 mm, and still more preferably a
value within the range of 1 .mu.m to 100 .mu.m.
[Third Embodiment]
As shown in FIGS. 7 and 8, the active-driving organic EL light
emission device 66 or 67 of a third embodiment comprises, on the
substrate 10, the TFT 14 embedded in the electrically insulating
film 12, the organic EL element 26 comprising the organic luminous
medium 24 between the upper electrode 20 and the lower electrode
22, the electrically connecting portion 28 for connecting the TFT
14 and the organic EL element 26 electrically to each other, and a
sealing member 58.
The third embodiment, wherein the upper electrode 20 comprises the
main electrode 16 and the auxiliary electrode 18 and further the
assistant element 18 in the upper electrode 20 is disposed in the
state that it is embedded in the sealing member 58 and caused to
penetrate through the sealing member 58 as shown in FIG. 7, or the
assistant element 18 is arranged in the state that it is closely
adhered to the sealing member 58 as shown in FIG. 8.
The following will describe the sealing member and the like in the
third embodiment, referring appropriately to FIGS. 7 and 8.
(1) Sealing Member
It is preferred that the respective sealing members 58 shown in
FIGS. 7 and 8 are arranged around the organic EL display devices 66
and 67 to prevent entry of water into the inside; or that a sealing
medium 21, for example, a desiccant, a dry gas, or an inert liquid
such as fluorinated hydrocarbon, is put into the thus-arranged
sealing member 58 and the organic EL display device 66 and 67.
This sealing member 58 can be used as a supporting substrate in the
case that the fluorescent medium or the color filter is arranged
outside the upper electrodes.
As such a sealing member, the same material as for the supporting
substrate, for example, a glass plate, or a plastic plate may be
used. An inorganic oxide layer or an inorganic nit-ride layer may
be used if it is superior in moisture-proofing. Examples thereof
include silica, alumina, AlON, SiAlON, SiN.sub.x
(1.ltoreq.x.ltoreq.2) and the like. The form of the sealing member
is not particularly limited, and is preferably, for example, a
plate form, or a cap form. When the sealing member is, for example,
in a cap form, the thickness thereof is preferably set to a value
within the range of 0.01 to 5 mm.
It is also preferred that the sealing member is pushed and fixed
into a groove and the like made in a part of the organic EL display
device or that the sealing member is fixed onto a part of the
organic EL display device with a photocuring type adhesive and the
like.
(2) Relationship Between the Sealing Member and the Auxiliary
Electrode
About the relationship between the sealing member and the auxiliary
electrode, it is preferred that the auxiliary electrode 18 is
arranged to be embedded in the sealing member 58 or to be closely
adhered to the sealing member 58 as shown FIGS. 7 and 8. Various
modifications are allowable.
Specifically, it is allowable to dispose a site where assistant
wiring 18 is set between an inner space made between the sealing
member 58 and the organic EL element 26, or to embed the auxiliary
electrode completely in the sealing member 58 and connect the
auxiliary electrode and the main electrode 16 electrically to each
other through via hole (which may be referred to as a through
hole).
[Fourth Embodiment]
A fourth embodiment is a method for manufacturing the
active-driving organic EL light emission device 61 of the first
embodiment shown in FIG. 1, and is specifically a method for
manufacturing the active-driving organic EL light emission device
61, characterized by forming, on the substrate 10, the TFTs 14
embedded in the electrically insulating film 12, the interlayer
insulating film 13, the lower electrodes 22, the organic luminous
medium 24, the upper electrodes 20 made of the main electrode 16
and the auxiliary electrode 18, and the electrically connection
portions 28 for connecting the TFT 14 and the organic EL element 26
electrically to each other.
That is, the fourth embodiment, comprising the steps of forming the
organic EL elements 26, forming the TFTs 14 embedded in the
electrically insulating film 12, forming the interlayer insulating
film 13, forming the lower electrodes 22, forming the organic
luminous medium 24, forming the upper electrodes 20 made of the
main electrode 16 and the auxiliary electrode 18, and forming the
electrically connection portions 28 for connecting the TFT 14 and
the organic EL element 26 electrically to each other.
The following will describe the characteristic portions and the
like thereof in the fourth embodiment, referring appropriately to
FIG. 12.
(1) Step of Forming the Thin Film Transistors (TFTs)
The step of forming the TFTs-14 (the step of forming the active
matrix substrate) will be described, referring to FIGS.
12(a)-(i).
1 Formation of an Active Layer
First, FIG. 12(a) shows the step of depositing an .alpha.-silicon
(.alpha.-Si) layer 70 on the substrate 10 by a method such as low
pressure chemical vapor deposition (LPCVD).
At this time, the thickness of the .alpha.-Si layer 70 is
preferably set to a value within the range of 40 to 200 nm. The
substrate 10 to be used is preferably a crystal material such as
crystal, and is more preferably low-temperature glass. When the
low-temperature glass substrate is used, the manufacturing process
is preferably carried out at a low-temperature process temperature,
for example, 1000.degree. C. or lower and more preferably
600.degree. C. or lower in order to avoid generation of melting or
strain in the whole of the manufacturing process or avoid
out-diffusion of dopants into an active area.
Next, FIG. 12(b) shows the step wherein the .alpha.-Si layer 70 is
irradiated with an excimer laser such as a KrF (248 nm) laser to
perform annealing crystallization, thereby converting the
.alpha.-Si to polysilicon (see SID '96, Digest of technical papers
pp. 17-28).
About annealing conditions using an excimer laser, it is preferred
that substrate temperature is set to a value within the range of
100 to 300.degree. C., and the energy amount of the excimer layer
rays is set to a value within the range of 100 to 300
mJ/cm.sup.2.
Next, FIG. 12(c) shows the step of patterning the polysilicon
crystallized by the annealing into an island form by
photolithography method. It is preferred to use, as an etching gas,
CF.sub.4 gas since superior resolution can be obtained.
Next, the FIG. 12(d) shows the step of depositing an insulating
gate material 72 on the surface of the resultant island-form
polysilicon 71 and the substrate 10 by chemical vapor deposition
(CVD) and the like, to prepare a gate oxide insulating layer
72.
This gate oxide insulating layer 72 comprises preferably silicon
dioxide to which chemical vapor deposition (CVD) such as plasma
enhanced chemical vapor deposition (PECVD: Plasma Enhanced Chemical
Vapor Deposition) or low pressure CVD (LPCVD) can be applied.
The thickness of the gate oxide insulating layer 72 is preferably
set to a value within the range of 100 to 200 nm.
Furthermore, substrate temperature is preferably 250-400.degree.
C., and annealing at 300-600.degree. C. for 1-3 hours is preferably
conducted to obtain a high-quality insulating gate material.
Next, FIG. 12(e) shows the step of depositing and forming a gate
electrode 73 by vapor deposition or sputtering. Preferred examples
of the constituent material of the gate electrode 73 include Al,
AlN and TaN and the like. The thickness thereof is preferably set
to a value within the range of 200 to 500 nm.
Next, FIGS. 12(f)-(h) show the steps of patterning the gate
electrode 73 and performing anodization. When Al gate is used,
anodization is preferably performed two times to attain insulation
as shown in FIGS. 12(f)-(h). Details of the anodization are
disclosed in Japanese Patent Application Publication No.
15120/1996.
Next, FIG. 12(i) shows the step of forming an n+ or p+ doping
region by ion doping (ion implantation), to form active layers for
a source and a drain. In order that the ion doping can be
effectively performed, it is preferred to introduce nitrogen gas
and perform heat treatment at 300.degree. C. for about 3 hours
during the ion doping.
On the other hand, it is preferred to use polysilicon made of
.alpha.-Si as the gate electrode 73. Specifically, the polysilicon
gate electrode 73 is formed on the gate insulating layer, and
subsequently an n type dopant such as arsenic is ion-implanted
thereto. Thereafter, a source region and a drain region can be
formed on the polysilicon island by photolithography method so that
they can be formed inside the polysilicon region.
The gate electrode 73 made of polysilicon can be supplied as a
bottom electrode of a capacitance.
2 Formation of the Signal Electrode Lines and the Scanning
Electrode Lines
Next, an electrically insulating layer, for example, SiO.sub.x
(1.ltoreq.x.ltoreq.2) is deposited on the resultant active layer by
ECRCVD method (Electron Cyclotron Resonance Chemical Vapor
Deposition method), and subsequently the signal electrode lines and
the scanning electrode lines (referred to as wiring electrodes) are
formed and electrical connection is attained. Specifically, the
signal electrode lines and the scanning electrode lines are formed
by photolithography method and the like, and upper electrodes of
the capacitances are formed. Performed are connection of the
sources of the second transistors (Tr2) 56 to the scanning
electrode lines; connection of the sources of the first transistors
(Tr1) 55 to the signal electrode lines; and the like.
It is preferred to form metal lines made of Al alloy, Al, Cr, W, Mo
and the like by photolithography method at this time and attain
contact of the drains and the sources of the first transistors
(Tr1) 55 and the second transistors (Tr2) 56 through openings of
the electrically insulating layer which are made from the side of
the entire surface thereof.
The thickness of the wiring electrode is preferably 50 nm or more,
more preferably 100 nm or more, and still more 100-500 nm.
3 Formation of the Interlayer Insulating Film
In the next step, the interlayer insulating film made of silicon
dioxide (SiO.sub.2), silicon nitride, polyimide and the like is
applied to the whole of the active layer and the electrically
insulating layer thereon.
The insulating film made of silicon dioxide can be obtained by
supplying, for example, TEOS (tetraethoxysilane) under the
condition of a substrate temperature of 250 to 400.degree. C.
according to PECVD. The film can also be obtained according to
ECRCVD at a substrate temperature of 100 to 300.degree. C. However,
it is preferred to use an organic interlayer insulating film since
these inorganic insulating films are not easily made flat.
(2) Step of Forming the Organic EL Elements
After the TFT structure and the interlayer insulating film are
formed as above, an anode (lower electrodes), an organic luminous
layer, a hole injection layer, an electron injection layer and the
like are successively formed thereon. Furthermore, a cathode (upper
electrodes) is formed so that the organic EL elements can be
produced.
For example, the lower electrodes are preferably formed using a
method making film-deposition in a dry process, such as vacuum
deposition or sputtering. About the organic luminous medium, it is
possible to adopt a commonly-known method such as vacuum
deposition, spin coating, Langumuir-Blodgett method (LB method), an
inkjet method, micelle electrolysis.
The auxiliary electrodes and the main electrodes are preferably
formed using vacuum deposition method, sputtering method and the
like. Specifically, it is preferred to form the main electrodes
made of transparent conductive material by vacuum deposition and
the like and then form the auxiliary electrodes made of
low-resistance material to make the upper electrodes.
It is preferred to form the auxiliary electrodes and simultaneously
connect them electrically to the connecting terminals of the TFTs.
It is also preferred that at this time an indium zinc oxide (IZO)
and the like, which is an amorphous oxide, as a connecting material
is interposed between the auxiliary electrode and the connecting
terminal of the TFT.
The organic EL element can be produced according to a reversible
order, that is, toward the side of the anode from the cathode
(lower electrodes).
Furthermore, it is preferred to form the organic EL element without
any break through the vapor deposition.
(3) Sealing Step and the Like
It is preferred that in the sealing step the organic EL elements
are formed and connected electrically to TFTs and subsequently
these are fixed with the sealing member to cover the periphery
thereof.
In the case that a direct-current voltage is applied to the organic
EL elements, the transparent electrode and the electrode are set to
polarities of + and -, respectively. In the case that 5-40 voltage
is applied to the organic EL elements, luminescence can be
observed. Thus, it is also preferred that the organic EL elements
are driven before the sealing step to judge whether the organic EL
elements obtained are good or bad.
INDUSTRIAL APPLICABILITY
According to the active-driving organic EL light emission device of
the present invention, the numerical aperture of pixels can be made
large even if the device has TFTs. The sheet resistivity of its
upper electrodes can be made low even if luminescence is taken out
from the side of the upper electrodes. Thus, images having a high
brightness and a homogenous brightness have been able to be
displayed.
According to the method for manufacturing an active-driving organic
EL light emission device of the present invention, it has become
possible to produce effectively an active-driving organic EL light
emission device that is low in the sheet resistivity of its upper
electrodes and that can take out luminescence from the side of the
upper electrodes and can display images having a high brightness
and a homogenous brightness.
* * * * *